1. Field of the Invention
This invention relates to a CVD (Chemical Vapor Deposition) apparatus to form a thin film on a semiconductor substrate by a CVD method using liquid reaction materials having a low vapor pressure. Particularly, it relates to the CVD apparatus with a liquid-source vaporization system that supplies a flow-controlled liquid reaction material after its vaporization.
2. Description of the Related Art
Up to this time, the CVD method has been widely adopted as a thin film formation method for a semiconductor apparatus. The CVD method is a method to form a thin film on a substrate by importing several types of gases selected according to the type of film to be formed into the reaction chamber and causing a chemical reaction by applying thermal energy or plasma excitation energy. In recent years, liquid reaction materials with low vapor pressure have attracted more attention for the reasons that they are excellent in covering and filling gaps or steps.
For example, Japan Patent Laid-open No.5-132779 discloses an apparatus that vaporizes a liquid reaction material to supply it to the reaction chamber. In this case, the liquid reaction material, the flow rate of which is controlled by a liquid flow rate controller, is atomized by an ultrasonic vibrator (circular vibrator depth-direction resonance type ultrasonic vibrator) placed in the atomization means, and then heated and vaporized with a heater.
However, according to the apparatus disclosed by Japan Patent Laid-open No. 5-132779, after the completion of the thin film formation processing, a liquid reaction material remains behind inside the ultrasonic vibrator, the casing of the atomization means, etc. The liquid reaction material residual within the ultrasonic vibrator drips and accumulates in the casing, and is soon atomized. The liquid reaction material gases remaining in the casing are denatured or degenerated through further heat. This will create the source of particle generation and will contaminate semiconductor substrates in the subsequent thin film formation process.
In particular, because Ta (OC.sub.2 H.sub.5).sub.5 which is one of the liquid reaction materials is decomposed at approximately 150.degree. C. (302.degree. F.), there is a high risk of creating a source of particle generation, if it remains in the casing.
Accordingly, an objective of the present invention is to provide a CVD apparatus equipped with a liquid-source vaporization system that does not leave any liquid reaction material within the system.
Another objective of the present invention is to provide a CVD apparatus with improved productivity by minimizing particle contamination.
In addition, another objective of the present invention is to provide a CVD apparatus equipped with a liquid-source vaporization system, which can perform cleaning work easily and quickly.
Furthermore, another objective of the present invention is to provide a CVD apparatus quipped with a liquid-source vaporization system, which can use various types of liquid reaction materials, regardless of their characteristics.